The present invention relates to an electric power generator, and more particularly, to an electrostatic induction type electric power generator that uses electret materials.
A compact electrostatic induction type electric power generator is known in the prior art. The electrostatic induction type electric power generator generates electric power by applying charges to electrodes of a variable capacitor, using the charges to generate Coulomb attraction force between opposing electrodes, and converting vibration energy into electric energy, in which the vibration energy is generated by vibrating a vibrator vibrates against the Coulomb attraction force.
FIG. 9 is a schematic cross-sectional view of a conventional electrostatic induction type electric power generator disclosed in Japanese Laid-Open National Phase Patent Publication No. 2005-529574. The electrostatic induction type electric power generator is a so-called electret electric power generator in which a first substrate 407 including conductive surface electrodes 411 and a second substrate 405 including electret material electrodes 409 are spaced from each other by a predetermined distance. The second substrate 405, which includes the electret material electrodes 409, is fixed and immovable. The first substrate 407 including the conductive surface electrodes 411 is connected to fixtures 417 by springs 419. The springs 419 are connected to two opposite sides of the first substrate 407. The elasticity of the springs 419 enables movement of the first substrate 407 in an X-axis direction 421 and returns the first substrate 407 to a neutral position after such movement. The overlapping area of the electret material electrodes 409, which carries charges, with the opposing conductive surface electrodes 411 increases and decreases as the first substrate 407 vibrates in the X-axis direction. This changes the charge of the conductive surface electrodes 411. The electrostatic induction type electric power generator uses the change in charge as electric energy to generate electric power.
However, in the electrostatic induction type electric power generator of FIG. 9, the substrate 407 vibrations are restricted in directions other than the X-axis direction 421. Thus, the electrostatic induction type electric power generator cannot use external vibrations in directions other than the X-axis direction 421 to generate electric power. Such an electrostatic induction type electric power generator thus cannot generate electric power when, for example, receiving external vibrations in a Y-axis direction, which differs from the X-axis direction 421.